The invention provides a portable device for detecting water or other foreign fluids in fuel tanks, particularly water in diesel fuel.
The invention provides a simple tethered tubular cartridge lowered into the fuel tank and having a pair of probe electrodes sensing a lower resistance current path through water present in the diesel fuel, and associated alarm circuitry. A top cap covers and seals the top end of the cartridge and secures an insulated electrical lead extending therethrough, and is configured for easy retrieval. A bottom cap covers and seals the bottom end of the cartridge and mounts and locates the probe electrodes, and includes a projection element preventing electrical shorting of the probe electrodes through a wall of the fuel tank.